Process for hydrodesulfurization of coker products



NOW 6, 1956 s. B. SWEETSER ET Al. 2,769,754

PROCESS FOR HYDRODESULFURIZATION oF coKER APRODUCTS Filed May 5, 1954IMZON PROCESS FOR HYDRODESULFURIZATION F COKER PRODUCTS Sumner B.Sweetser, Cranford, and `lohn Weikart, Westfield, N. J., assignors toEsso Research and Engineering Company, a corporation of DelawareApplication May 3, 1954, Serial No. 427,281

3 Claims. (Cl. 196-24) This invention is concerned with an improvedprocess for the manufacture of high quality petroleum oil products. Theinvention is more specifically concerned with the treatment of streamsderived from heavy residual coking operations. In accordance with aspecific adaptation of the present invention, petroleum oil productssecured from heavy residual coking operations are desulfurized in ahydrogen treating Zone wherein the constituents boiling in the motorfuel boiling range and the constituents boiling in the gas oil boilingrange are processed -together in a mixed liquid-gas phase operation. Ina preferred adaption of this invention the hydroiined products arewithdrawn from an initial hydrodesulfurization zone and passed to a hotseparator zone wherein lower boiling constituents such as those boilingin the motor fuel and light gas oil boiling ranges are removed in thevapor phase, and wherein the higher boiling constituents such as thoseboiling above the light gas oil boiling range are removed as a liquidphase. This liquid phase is withdrawn and passed to a secondaryhydrodesulfurization zone operated under operating conditions adapted tosecure the desired degree of desulfurization.

In Ithe hydrodesulfurization of petroleum streams it is very desirablethat the operating conditions employed for the hydrodesulfurization ofconstituents boiling in the motor fuel boiling range be appreciablydifferent from the operating conditions employed for thehydrodesulfurization of constitutents boiling above the motor fuelboiling range as, for example, boiling in the heating oil and gas oilboiling ranges. the hydrodesulfurization of a heavy naphtha fractionboiling in the motor fuel boiling range are vin the range from about 650F. to 700 F. Pressures generally are in the range from about 200 lbs.per square inch to 400 lbs. per square inch. The feed rates are usuallyin the range from about 2 to 8 volumes of oil per volume of catalyst perhour. This typical heavy naphtha fraction boils in the range from about250 F. to 430 F. On the other hand, when hydrodesulfurizing a gasoilboiling in the range from about 430 F. to l050 F., the tempera-turesare usually in the range from about 675 F. to 800 F., preferably in therange from about 700 F. to 750 F. Pressures are about 200 lbs. persquare inch to 1000 lbs. per square inch, preferably in the range from200 lbs. per square inch to 400 lbs. per square inch. The feed ratesusually are about 0.5 to 2.0 volumes of oil per volume of catalyst perhour.

The catalyst may comprise a mixture, of cobalt oxide and molybdenumoxide on alumina. A preferred catalyst comprises about 12% cobaltmolybdate on alumina. Other satisfactory catalysts are sultides ofnickel and tungsten alone or on an alumina support.

Also with respect to naphtha and gas oil fractions derived from thecoking of heavy residual fractions as, for example, those residualshaving gravities below about 15 A. l". I., a particular problem arises.While the processing of these coker fractions boiling above about 400 F.in a hydrodesulfurization can be satisfactorily Typical temperaturesemployed for States Patent 0 850 F. to 1050 F. in the coking zone.

` ing stream of finely divided coke particles to furnish heat and alarge amount of surface to accomplish the coking reaction. The operationrequires the use of a burner vessel and a reaction vessel with thenecessary standpipes and transfer lines to accomplish the circulation ofiluidized coke between the two vessels. The fluidized coke iscontinually formed in the process and it is partly burned to supplyheat. The bulk of the coke is withdrawn from the system as a by-product.

The feed to the coking operation is usually a bottoms -stream from avacuum distillation operation and may comprise from about 4% to 50% ofthe crude depending upon the source and character of the crude. Thetemperatures employed in the coking operation may vary appreciably butare generally in the range from about rlhe pressures in the coking zoneare generally in the range from about 5 lbs. per square inch to 50 lbs.per square inch. The temperatures in the burning zone are in the rangefrom about 1100 F. to l200 F. while Ithe pressures are in i the rangefrom about 15 lbs. per square inch to 50 lbs. per

square inch.

The products secured from a uid coking operation processing high sulfurresidual stock are high in sulfur and are relatively unstable. However,hydrodesulfurization provides a satisfactory means of converting the rawunstable coker products into iinished low sulfur products with goodstability. Hydrodesulfurization of Coker gas oil (fboiling in the rangefrom about 430 F. to 1050 F.) can be accomplished without difficulty.However as mentioned heretofore, hydrodesulfurization of cokerconstituents boiling in Ithe motor fuel range due to the presence ofunsaturated constituents is highly exothermic. The heat liberated tendsto give a marked temperature rise during the reaction, making theoperation difficult to control.

In accordance with the broad aspect of the present invention a blend ofcoker naphtha and coker gas oil are hydrodesulfurized in a mixedvapor-liquid phase process. When operating in this manner thetemperature rise in the reactor is minimized by 4the high heat capacityof the liquid phase gas oil and by the tendency of this gas oil tovaporize further as the temperature tends to rise. However, onedisadvantage is that the octane number of motor fuel is impaired. Thisis not a disadvantage when loss of octane number of the naphtha is notof importance,

as for example when the naphtha is used as feed to a hydroformingoperation or as diesel fuel. As mentioned, the hydrodesulfurization ofthe blend does have the typical disadvantage of treating a wide boilingrange feed stock.

.The conditions required for the hydrodesulfurization of the gas oil areoverly severe for the hydrodesulfurization of the naphtha to be blendedin motor gasoline. In accordance with the speciiic concept of thepresent inven tion these disadvantages are overcome.

The process =of the present invention may be fully understood byreference to the attached drawing illustrating one embodiment of thesame wherein a Coker product stream is processed. Referring specificallyto the drawing a heavy residual fuel as, for example, one boiling aboveabout 1000o F. and having a gravity in the range from patented Nov. 6,1956 about A. P. I. to 20 A. P. I. is introduced into the coker reactionzone by means of feed line 11. Steam is introduced into zone 1t) bymeans of line 12 which maintains thc particles of coke in a iiuidizedstate. Coke particles are withdrawn fnom the bottom of coking zone 10 bymeans of line 14 and passed lto a burner zone (not shown). In the burnerzone portions of the coke particles are burned and a portion of theheated coke particles are returned by conventional means of line 60 tocoker zone 10. The coker zone 10 is operated at a temperature in therange from about 850 F. to 1100 F. and at a pressure in the range fromabout to 50 lbs. per square inch.

Vaporized products are removed overhead from Coker zone 10 by means ofline 15 at a temperature in the range from about 850 F. to 1100 F. Thereproducts are passed through a partial condenser zone 16. These cooledproducts are passed to distillation zone 17 wherein a stream comprisinghydrocarbons boiling in the motor fuel range and in the gas oil rangeare segregated by means of line 18. Higher boiling hydrocarbons areremoved by means of line 19 and may be recycled to coker zone 10.

The products removed by means of line 18 are introduced into aseparation or distillation zone 20. The separator is operated to removeoverhead by means of line 21 light hydrocarbon constituents boilingbe-low about Z50-275 F. These overhead constituents are passed through acooling zone 22 and then introduced into a separator zone ordistillation 23. In separation zone 23 water is removed by means of line24, uncondensed gases by means of line 25 and a light coirer naphtha bymeans of line 26.

A liquid stream comprising heavy naphtha constituents and constituentsboiling labove the motor fuel boiling range is removed from separator bymeans of line 27, passed through furnace or equivalent means 28 andintroduced into an initial hydrcdesulfurization reactor 29 by means ofline 30. The temperature of the stream removed from furnace 28 is in therange from about 500 F. to 800 F. Fresh hydrogen may be introduced bymeans of line 31 while recycle hydrogen may be introduced by means ofline 39.

Hydrodesulfurization zone 29 is operated at a temperature in the rangefrom about 500 F. to 800 F. and at a pressure in the range from about100 to 1000 p. s. i. g. The feed rate is in the range from about 0.5 to4.0 volumes of Voil per volume of catalyst per hour. The catalystpreferably comprises cobalt molybdate supported on alumina.

The treated product is removed from the initial hydrodesulfuriza'tionzone 20 by means of line 32 and passed through partial condenser zone 61and into a hot separator zone 33. This zone is operated undertemperature and pressure conditions to remove overhead by means of line34 hydrocarbon constituents boiling below about 450- 800 Thesehydrocarbon constituents are passed through a cooling zone 35 andintroduced into a separator or distillation zone S6. Hydrogen is removedoverhead from separator 36 by means of line 37 and compressed in zone3S. Hydrogen sulfide is removed in zone 62 prior to recycling thehydrogen by means of line 39. Hydrogen may be purged from the system bymeans of line 63. Hydrocarbon constituents boiling in the motor fuel andheating oil boiling ranges are removed from zone 36 by means of line d2.

Higher boiling hydrocarbon constituents such as those boiling in thc oilboiling range are removed from hot separator 33 by means of line 40.These constituents boil above about 430 F., preferably above about 700F. to 730 F In accordance with the present invention these constituentsare passed through heat exchange zone 64 and are then passed to asecondary hydrodesulfurization zone 41. Zone di is preferably operatedat a temperature between about 675 F. and '000 F. and at a feed rate of0.5 to 2.0 volumes of oil per volume of catalyst per hour. The

temperature of the stream in zone 64 is raised or lowered depending onthe inlet temperature desired in hydrodesulfurization zone 41. Freshhydrogen is added by means of line 50 While recycle hydrogen may beadded by means of line 65. It is preferred to add all the fresh hydrogento the process through line 50 and to employ only recycle hydrogen inthe initial desulfurization zone 29. The hydrodesulfurized higherboiling hydrocarbons are re moved from zone 4I by means of line 43,cooled by means not shown and introduced into zone 51. Hydrogen isremoved by means of line 66 while the hydrodesulfurized heavy product isremoved from zone 51 by means of line 67.

In accordance with the present invention the hydrocarbon productssegregated by means of lines 42 and 67 are passed to a distillation zone63, wherein a segregation of the desired products as, for example, motorfuels and heating oils are made. Hydrocarbon constituents boiling belowthe motor fuel boiling range and hydrogen sulfide are removed by meansof line 45, hydrocarbon constituents boiling in the motor fuel boilingrange are removed by means of line 46, hydrocarbons boiling in the gasoil `boiling range are removed by means of line 47 while higher boilinghydrocarbon constituents are segregated by means of line 48.

The present process is broadly concerned with an operation whereinhydrocarbon constituents boiling in the motor fuel boiling range F. to430 F.) are hydrodesulfurized with gas oil constituents boiling abovethe motor fuel boiling range (430 F. to 1050 F.) in a mixed vapor-liquidoperation. In this operation it is preferred to pass a heavy naphthafraction and gas oil fraction boiling up to about l050 F. through aninitial hydrodesulfurization zione. The hydrodesulfurized product isremoved from the initial hydrodesulfurization zone, passed through apartial condenser and into a hot separator zone wherein hydrocarbonconstituents boiling below about 450 F. to 800 F. are removed overheadas a vapor stream. The higher boiling constituents are removed as aliquid stream and passed through a secondary hydrode- `ulfurizationzone.

The latter liquid stream comprises constituents boiling above about 700F. to 730 F. and is passed to the secondary hydrodesulfurization zonewherein conditions are adapted to secure efiicient hydrodesulfurizationof the high boiling stock. In general, the temperature is in the rangeof about 675 F. to 800 F., preferably in the range from about 700 F. to750 F. Pressures are in the range of from about 200 to 1000 lbs. persquare inch guage while the feed rate is preferably in the range from0.5 to 2.0 volumes of oil per volume of catalyst per hour. Thehydrodesulfurized products from both zones are preferably passed to adistillation zone wherein the desired final product streams aresegregated as desired.

What is claimed is:

1. Process for the hydrodesulfurization of hydrocarbon constituentsboiling in the motor fuel boiling range and hydrocarbon constituentsboiling in the gas oil boiling range, both of which are derived by thecoking of heavy residual petroleum fractions, which comprises passing acombined stream of these constituents and added hydrogen through aninitial hydrodesulfurization zone in a mixed liquid-gas phase operation,maintaining said initial zone at a temperature in the range of fromabout 650 to 700 F., withdrawing the product from said initial zone andpassing the same to a hot separation zone wherein hydrocarbonconstituents boiling below about 400 to 750 F.- are segregated as avapor phase, passing said vapor phase to a separator and removinghydrogen therefrom, removing from said hot separation zone a liquidphase comprising hydrocarbon constituents boiling above about 400 to 750F., and passing said liquid phase by itself, together with addedhydrogen, through a secondary hydrodesulfurization zone, maintainingsaidl secondary zoneat aA temperature in the range of 5 from about 700to 750 F., removing the product from said secondary hydrodesulfurizationzone, separating hydrogen therefrom, combining the respectivehydrodesulfurized streams and segregating a fraction boiling in themotor fuel boiling range and a fraction boiling in the gas oil boilingrange.

2. Process as defined by claim 1 wherein said hydrocarbon constituentsboiling in the motor fuel boiling range boil in the range from about 250to 430 F.

3. Process as defined by claim 1 wherein said stream segregated as avapor phase in said hot separator has a nal boiling point in the rangefrom about 600 to 700 F.

References Cited inthe le of this patent UNITED STATES PATENTS

1. PROCESS FOR THE HYDRODESULFURIZATION OF HYDROCARBON CONSTITUENTSBOILING IN THE MOTOR FUEL BOILING RANGE AND HYDROCARBON CONSTITUENTSBOILING IN THE GAS OIL BOILING RANGE, BOTH OF WHICH ARE DERIVED BY THECOKING OF HEAVY RESIDUAL PETROLEUM FRACTIONS, WHICH COMPRISES PASSING ACOMBINED STREAM OF THESE CONSTITUENTS AND ADDED HYDROGEN THROUGH ANINITIAL HYDRODESULFURIZATION ZONE IN A MIXED LIQUID-GAS PHASE OPERATION,MAINTAINING SAID INITIAL ZONE AT A TEMPERATURE IN THE RANGE OF FROMABOUT 650* TO 700* F., WITHDRAWING THE PRODUCT FROM SAID INITIAL ZONEAND PASSING THE SAME TO A HOT SEPARATION ZONE WHEREIN HYROCARBONSCONSTITUENTS BOILING BELOW ABOUT 400* TO 750* F. ARE SEGREGATED AS AVAPOR PHASE, PASSING SAID VAPOR PHASE TO A SEPARATOR AND REMOVINGHYDROGEN THEREFROM, REMOVING FROM SAID HOT SEPARATION ZONE A LIQUIDPHASE COMPRISING HYDROCARBON CONSTITUENTS BOILING ABOVE ABOUT 400* TO750* F., AND PASSING LIQUID PHASE BY ITSELF, TOGETHER WITH ADDEDHYDROGEN,